96 GTX - Buy or not to buy?

[mejim707]

Those older 787 engines have a labyrinth seal on the crankshaft that keeps the oil from seeping into the cylinders from the rotary valve shaft, they almost all leak from age, resulting in the cylinder filling up with oil when sitting in the garage when not being used. Plan on swapping the crank too while your in there and make sure you rebuild the carbs 100% correctly, clean the entire fuel system out, buy a new fuel selector valve and you should have a good running trouble free ski.

Thanks!

So, wouldn't I be able to see oil build up if that was the case? Also, if I do the crank I may as well replace the entire engine.

Before breaking the case apart and replacing the crank I'd like to first determine if it's necessary somehow. How do you suggest I can determine that?

Thanks

 

[acooper]

I never buy a machine to turn over for a profit, I only do it because I want the machine and enjoy learning to work on them, I can always sell them for more than I have into them but if I were to figure in the time that I have invested I would normally be further ahead just working those hours.

To burtshaver2021
You have got that exactly right, my man (in my opinion).
Buying to resell always sounds GREAT (cars, trucks, boats, whatever) until it doesn't.
Buying it to get it running right? for the satisfaction? for a job well done? absolutely.

 

[drnickv]

If you pull the motor, you have to align it. That is a 300 tool. I understand SBT is junk for motor parts. I would do some research. Seadoo Engines gives a unconditional 2 year warranty if they rebuild i. I went that way. It always costs twice as much and takes twice as long. That is my mantra and rarely does it let me down!

 

[etemplet]

Thanks!

So, wouldn't I be able to see oil build up if that was the case? Also, if I do the crank I may as well replace the entire engine.

Before breaking the case apart and replacing the crank I'd like to first determine if it's necessary somehow. How do you suggest I can determine that?

Thanks

Easy enough to put 5 psi on the rotary valve chamber and see if it leaks at all. Just be careful NOT to over pressure those lip seals. I pressured one up and found leaks at the case partings. I peened them gently and got them to seal. It was leaking air but might not have leaked oil. Remember that.... air is a different test that oil and that must be considered if the leak is very very slight.

 

[mejim707]

Easy enough to put 5 psi on the rotary valve chamber and see if it leaks at all. Just be careful NOT to over pressure those lip seals. I pressured one up and found leaks at the case partings. I peened them gently and got them to seal. It was leaking air but might not have leaked oil. Remember that.... air is a different test that oil and that must be considered if the leak is very very slight.


View attachment 64362

Ah ok, so I can get the block off plate kit and pressurize to about 5PSI and if there are no leaks then I shouldn't have to pull the entire engine apart?

Any insight on how to see if the crank needs to be replaced?

Thank you again!

 

[burtshaver2021]

Ah ok, so I can get the block off plate kit and pressurize to about 5PSI and if there are no leaks then I shouldn't have to pull the entire engine apart?

Any insight on how to see if the crank needs to be replaced?

Thank you again!

I’m regards to the leak down test for the crankcase I have just used an old inner tube and sandwiched it in between the carb and intake and between the tuned pipe and exhaust manifold. Works good if you can’t find it don’t want to buy or build a block off kit

 

[etemplet]

I was not referring to the engire crankcase just the rotary valve chamber. All that takes is a crimped hose on one end and a pressure hose on the other. The Crankcase can be tested as well. Good luck !!

 

[mejim707]

I picked up the ski over the weekend. I'll be pulling the motor this weekend.

I spoke to the kid who used to ride it. He said this always bogged down and would just shut off.

Since this still has those gray lines, that totally sounds to me like clogged carbs from the infamous sludge!

We shall see, I'll report back and share some pics along the journey.

 

[burtshaver2021]

Looking forward to following along

 

[etemplet]

About all you can do with the crankshaft is check movement on the crank rod bearings and feel for roughness on the crank bearings as you rotate it. That is gonna be relative to your experience. I've heard some noise at times that I didn't like but found a new crank sounded the same. Absence of oil will do the same. If you feel bumps or any difficulty in turning the crank or rod bearings hanging up the crank needs to be redone. You can split the cases and buy a full gasket kit. That will allow you to inspect more closely the crank bearings and the balance shaft bearings. This is what it looks like. Good Luck.

 

[mejim707]

I pulled the engine today and started breaking it down. A few observations;

• The case to jug gasket has a tear in it for whatever reason.
• The PTO cyl has obvious signs of scoring on the piston, but almost no signs of damage on the cylinder walls.
• The PTO piston oil ring was jammed on one side.
• The PTO side, down in the case, has a lot of oil in it. It's about half full of oil.
• The MAG cylinder and piston has no sign of any issue. Which is strange because that side had low compression. Perhaps the torn gasket on that side was a contributing factor. It's hard to say though because the tear was on the outer edge.
• The crank rotates perfectly smooth. It has no signs of play and makes no sound while rotating.

At this point I think I have no choice but to crack the case open and replace seals. I don't know why this amount of oil would be present in the case.

Tear in gasket:


Both pistons looks good. No melting:


PTO side, is half full of oil:

 

[etemplet]

If that is full of oil you need to replace the crank. Your inner seals are leaking. Great engine when you get it right. Good Luck !!

 

[mejim707]

If that is full of oil you need to replace the crank. Your inner seals are leaking. Great engine when you get it right. Good Luck !!

Ah bummer. So if there’s oil in there the crank is bad. These engines are strange. So the crank only gets lubrication by suction across the crank when air/fuel/oil gets drawn into the cylinders? Do I have that right?

This would also explain the wear on the PTO piston, and why the mag had poor compression. While the PTO side was moving through the oil, it would slow the MAG side (Low Compression due to slow movement) and cause added force / drag on the PTO side pressing the piston with too much force against the cylinder wall.

At this point I may be better off just buying an engine then. The crank is about $400 and the top end is $500 plus $70 gasket kit and other odds and ends. That’s almost the price of a fully built engine. I have no beef with that. I offloaded some old items which pays for the engine so it’ll be free essentially.

 

[etemplet]

Yea parts are the price of an engine but delivery is the issue and of course quality. If you do it yourself it will be done right and you control the time frame. You give the engine to a vendor and who knows. I deal with SES and you never know when you are getting it back. LOL Plus you gotta do half the work taking everything apart then reassembling the engine. All they do is swap parts and you have to check their work. Good Luck !!

 

[burtshaver2021]

Ah bummer. So if there’s oil in there the crank is bad. These engines are strange. So the crank only gets lubrication by suction across the crank when air/fuel/oil gets drawn into the cylinders? Do I have that right?

This would also explain the wear on the PTO piston, and why the mag had poor compression. While the PTO side was moving through the oil, it would slow the MAG side (Low Compression due to slow movement) and cause added force / drag on the PTO side pressing the piston with too much force against the cylinder wall.

At this point I may be better off just buying an engine then. The crank is about $400 and the top end is $500 plus $70 gasket kit and other odds and ends. That’s almost the price of a fully built engine. I have no beef with that. I offloaded some old items which pays for the engine so it’ll be free essentially.

Just curious, how long was the machine sitting for? If it was an extended period of time perhaps the oil leak past the Center seal is not to severe? I have a 95 Xp that will leak a little over the winter but once the riding season comes and it’s started at least once w wry 2 weeks it’s not enough to cause any issues. Since you haven’t had the machine long I guess there’s no way for you to know how quickly it leaks past so it would be a bit of a risk but if the crankshaft spins nicely you could possibly use it with very little issue as is

 

[etemplet]

On a number of skis with inner seal leaks I have just installed a cut of valve and have had great success. My wife's ski has had a valve for 4 years and it works great and runs great. As @burtshaver2021 said you need to determine how bad a leak you have. With the engine out you can pressurize the rotary valve cavity and determine if you have a leak at all. Best check. Good Luck !!

 

[mejim707]

Oh interesting! I will definitely try pressurizing the cavity tomorrow to see what's up. It's pretty full of oil on the PTO side, and it's been sitting for a number of years before I got it. And based on the look of this thing, I don't think it's had much use. It's likely sat most of it's life.

 

[etemplet]

Sitting that long the parts may not last anyway but you might get lucky. For the test I'd only put around 5psi on the rotary chamber. I'd also get the oil out of casing and clean it up before testing. Good luck !

 

[burtshaver2021]

I would do a leak down test as well to determine if the outer seals are leaking so they can be changed while you have the engine on the bench if needed. See how your pressure test goes on the RV cavity, if it where me I would chance it and keep the existing crank but that’s just me. I haven’t suffered a crank failure yet so maybe my opinion will change when that day comes

 

[mejim707]

So, I will absolutely do this. I'll crack the case open today and replace those seals and clean it up real nice in there.

However, how would I ever know if the crank is ok or not? Rotating it by hand it's smooth as silk. No rubbing or sound whatsoever.

Perhaps it leaked during the extended storage time and maybe it was never run like this? I don't know. But if there's a way to review the crank to determine if it needs a replacement or not, please let me know. I will absolutely do that.

Thanks all!

 

[burtshaver2021]

So, I will absolutely do this. I'll crack the case open today and replace those seals and clean it up real nice in there.

However, how would I ever know if the crank is ok or not? Rotating it by hand it's smooth as silk. No rubbing or sound whatsoever.

Perhaps it leaked during the extended storage time and maybe it was never run like this? I don't know. But if there's a way to review the crank to determine if it needs a replacement or not, please let me know. I will absolutely do that.

Thanks all!

Let’s see what etemplet says, he’s got a lot of experience with them, myself I’ve only ever rotated them to see how smooth they roll and listened for any noise that I thought shouldn’t be there, so far I e been lucky, but it’s just that, luck cause I’ve never came across a bad one yet so I don’t even know what a bad one sounds or feels like.

 

[mejim707]

Let’s see what etemplet says, he’s got a lot of experience with them, myself I’ve only ever rotated them to see how smooth they roll and listened for any noise that I thought shouldn’t be there, so far I e been lucky, but it’s just that, luck cause I’ve never came across a bad one yet so I don’t even know what a bad one sounds or feels like.

Yeah makes sense, but I'm not gunna lie, I wouldn't mind doing a full rebuild on the engine. It'll be my first complete rebuild down to the crank, so just for the sake of knowledge, I would like to.

But I don't want to drop $400 on a new crank without knowing it's actually needed. I also don't want to reuse this crank if it'll fail. I'm sure he has a good way to verify the crank status.

 

[burtshaver2021]

Yeah makes sense, but I'm not gunna lie, I wouldn't mind doing a full rebuild on the engine. It'll be my first complete rebuild down to the crank, so just for the sake of knowledge, I would like to.

But I don't want to drop $400 on a new crank without knowing it's actually needed. I also don't want to reuse this crank if it'll fail. I'm sure he has a good way to verify the crank status.

I like your way of thinking, I also am looking forward to getting into a crank. I’m pretty sure I will need to with this 98 Challenger I picked up, the one engine is seized solid.

 

[etemplet]

Test the rotary valve chamber "before" you disassemble the engine. If you are concerned about the outter seals in the engine case I'd just test the case as well. No sense in opening a can of worms and creating problems unless you need to. I got a bunch of those lip seals brand new. Cheaper for me to buy the full gasket set than the gaskets I need so I end up with a lot of new parts.

 

[mejim707]

Test the rotary valve chamber "before" you disassemble the engine. If you are concerned about the outter seals in the engine case I'd just test the case as well. No sense in opening a can of worms and creating problems unless you need to. I got a bunch of those lip seals brand new. Cheaper for me to buy the full gasket set than the gaskets I need so I end up with a lot of new parts.

So I’ve already removed the jugs, but I think i should be able to test the rotary cavity even in this state. I’ll drain the oil out of the case first though. I’ll pressurize to 5 PSI, no more, and see what happens!

Thank you!